Restructuring and Severance Charges - Restructuring Activities and Accrued Liabilities (Details) $ in Millions	3 Months Ended
	Dec. 31, 2017 USD ($)
Restructuring Reserve [Roll Forward]
Beginning Balance	$ 18.6
Provisions	5.8
Reversal/adjustment of prior provision	(0.3)
Cash expenditures	(6.0)
Other non-cash settlement	(1.7)
Ending Balance	16.4
Employee Severance
Restructuring Reserve [Roll Forward]
Beginning Balance	8.5
Provisions	4.5
Reversal/adjustment of prior provision	0.1
Cash expenditures	(4.7)
Other non-cash settlement	0.0
Ending Balance	8.4
Contract Termination Costs
Restructuring Reserve [Roll Forward]
Beginning Balance	8.4
Provisions	0.8
Reversal/adjustment of prior provision	(0.2)
Cash expenditures	(1.3)
Other non-cash settlement	(0.8)
Ending Balance	6.9
Other Associated Costs
Restructuring Reserve [Roll Forward]
Beginning Balance	1.7
Provisions	0.5
Reversal/adjustment of prior provision	(0.2)
Cash expenditures	0.0
Other non-cash settlement	(0.9)
Ending Balance	$ 1.1